In the field of position measuring systems, optical systems are sometimes employed. The optical system is remotely located from the position occupied by the object of interest, and where the object of interest is a source of radiant energy, a passive optical system may be employed to measure the position of the object. Prior passive optical systems are complicated and costly, or provide measurements that are unreliable or ambiguous and require experienced interpretation by the operator. The present invention is a simple and straight-forward technique for measuring the position of a source of optical radiation within the field of view of the system, and provides outputs that are easily processed to provide direct measurements of the object's position.
The present invention employs first and second channels, with each converting the field of view into an electrical signal that is coupled to a common gated divider. The physical difference between the two channels is that the moving slit aperture of the second includes a linear, spatially varying filter. It attenuates that channel's detection of the image of the object of interest when the filter is moved into an overlaying relationship with the image. The output of the gated divider is zero because the output of channel Y is below the threshold of G until the apertures pass over the images, at which time the output becomes non-zero, with the value being dependent on the lateral position of the object in the image because of the difference between the invariant attenuation factor of the first and the linearly varying attenuation factor of the second. Then, a pulse is provided by the gated divider. In this manner, by noting the position of the apertures, one coordinate of the object may be measured, such as elevation. And, by noting the ratio of the outputs, the second coordinate may be measured, such as azimuth. Together, the coordinates define the object's position within the system's field of view. Additionally, when more than one source may be within the system's field of view, the relative amplitudes of the sources can be identified and employed to insure that the coodinates that are measured for one source are not confused with the coordinates measured for another.